Photographic products containing magnetic particles and processes therefor



Nov. 17,1964 r. BBo'rr ETAL 3,157,500

PHOTOGRAPHIC DU CONTAINING MAGNETIC PARTIcLEs AND cEsSEs THEREFOR Filed Sept. ll, 1962 2 Sheets-Sheet 1 lg 12X 13W' I Figz Fign

Thomas LAbbott .Edwin B.Wyand IN VEN TORS L5 @Mx Nov. 17, 1964 T. l. ABBOTT ETAL 3,157,500

PHOTOGRAPHIC PRODUCTS coNTAINING MAGNETIC PARTICLES AND PROCESSES THEREFOR Filed Sept. ll, 1962 2 Sheets-Sheet 2 Figa Thornans` IJlbbolt Edwin nwyand INVENTORS' Unted States Patent 3,157,500 PHGTGGRAPHIC PRODUCTS CGNTAINING MAG- NETIC PARTCLF AND PROCESSES THEREFR Thomas Abbott and Edwin B. Wyand, Rochester, N,Y.,

assignors to Eastman Kodak Company, Rochester,

N.Y., a corporation of New Jersey Filed Sept. 11, 1962, Ser. No. 222,861 8 Claims. (Ci. 96-28) This invention relates to the preparation of novel photographic materials and the methods of forming images therefrom.

U.S. Patent 2,819,963, issued January 14, 1958, to Hamm, discloses a method of making photographic resist materials in which a ferromagnetic iron oxide, such as y-ferric oxide (Fe203) is uniformly dispersed in a photographic gelatino-silver-halide emulsion and the mixture is coated uniformly on the surface. The photographic emulsion is then exposed in the usual manner and processed to a relief image. The relief image thus formed is magnetized or sensed using a recording head so that the relief image is also a magnetic image. The magnetic latent image is then developed to a magnetic visible image using a finely divided iron (ferromagnetic). Copies are then obtained by contact transfer, such as using a moist, pressure-sensitive adhesive transfer material, such as dye transfer paper.

The process described in the Hamm patent requires magnetic particles which possess the ability to become permanently magnetized, i.e., particles having a high-magnetic susceptibility. This process also requires that the Y normal process be carried out, including the step of Washing with hot water sprays to remove the unhardened portions of the emulsion.

It has been desired to provide a stable image producing a process which would be simple in nature and which would provide high-speed processing.

We have discovered a process in Which a photographic emulsion is used which contains developing agents and ferromagnetic particles of high magnetic permeability and of low magnetic susceptibility as Well as gelatin, silver halide grains, etc., which can be rapidly stabilized by removing the untanned areas of the emulsion by magnetic attraction.

One object of this invention is to provide images without the use of hot Water sprays. Another object of this invention is to provide means for obtaining positive and negative images simultaneously. An additional object is to provide a visible image which can also be scanned by electromagnetic means. A further object is to provide a printing plate for the printing of magnetic inks. An additional object is to provide high density photographic images with only a small amount of silver halide incorporated in the photographic sheet. Still another object is to provide extremely simple processing means. A further object is to provide means for the rapid processing of photographic images obviating the need for additional fixation or stabilization of either image. A still further object is to provide means for obtaining continuous tone images under simple and rapid processing conditions.

In the accompanying drawings, FIGURE l shows a schematic exaggerated cross-section of a photosensitive sheet embodying one form of this invention. FIGURE 2 shows a representation of the same film cross-section resulting from the development action, and FIGURE 3 represents the image obtained on the photosensitive sheet at the end of the process. FIGURES 4, 5, and 6 indicate three means by which the process of this invention is accomplished.

FIGURE 1 shows a photosensitive gelatin layer 1li, coated on a clear film support 11 which contains the ice silver halide particles 12, the ferromagnetic particles 13, and particles of developing agent 14. The developing agent may be dispersed throughout the gelatin layer or may be added thereto as an oily liquid dispersion. FIG- URE 1 also shows, for 'the purpose of explaining the subsequent flgures, the exposure of the flrn element to a mask 1S..

In FIGURE 2 is shown the cross-sectional element of FIGURE 1 after exposure and development have taken place. Some of the silver halide grains 12, such as grain 16, have become reduced to metallic silver. The formation of oxidized developing agent in the vicinity of the reduced silver halide grains has caused a tanning of the gelatin binder in these areas as indicated by the shaded portion 17. The tanned gelatin 17 binds tightly the reduced silver grains i6 and the magnetic particles 13.

By the application of a magnetic force to the emulsion side of this iilrn section, as achieved by passing the sheet through a region of high non-uniform flux, the untanned gelatin is removed together With the solid and liquid components held therein. VThe result of this removal on the cross-sectional element is shown in FIGURE 3.

One method of removing the untanned lgelatin from the photosensitive sheet is illustrated in FIGURE 4, in which the emulsion surface of the magnetic relief film is drawn across a pole of the electromagnet 18. With this method, the pole piece of the magnet must be cleaned regularly of accumulated magnetic emulsion.

Our preferred method for accomplishing 'the process of this invention is shown in FIGURE 5. As represented in cross-section, a long strip of paper web Sti is drawn through the activator solution 31 by means ofroller 27 set in the tank 28. The activator-laden web 30 is brought in contact with the emulsion side of the photomagnetc film 29 bymeans of a pair of vvWringer rollers 25 and 26. The sandwich of film and web then travels to the vicinity of the magnet 20 during which time development and vtanning takes place in the photosensitive emulsion. In

the magnetic field of the pole elements 21 and 22 where the flux density is rapidly changing, the untanned emulsion of the sheet 29 is stripped to the web 30' with the aid of roller 24. After stripping the magnetic relief lm 2li holds negative image comprising silver and magnetic particles in tanned gelatin, while the web 30 holds a positive image initially comprising silver halide and magnetic particles in untanned gelatin.

FIGURE 6 indicates an arrangement of pole pieces which would make a more ecient use of the field strength than that shown in FIGURE 5. Like elements are numbered identically in FIGURES 5 and 6.

In carrying out our invention magnetic particles are incorporated in the photographic emulsion of the selfdeveloping type as referred to in U.S. Patent 2,592,368. 'After exposure and development of the photographic image containing the magnetic particles, the untanned gelatin-silver halide emulsion is removed by magnetic effects in place of the Warm Wash. In carrying out the processing of our photographic emulsion, a wet paper web containing an aqueous alkaline solution is brought vin contact with the unhardened exposed photosenstive layer containing a tanning developing agent.

A magnetic attraction is exerted by a magnetic means through the Wet paper web to attract the ferromagnetic particles in the undeveloped areas of the photographic image tothe receiver surface at the same time that vthe two surfaces are parted and stripping occurs. When the paper receiver holding the thus removed image from the photosensitive sheet is dried, a permanent bond between the paper and removed gelatin is obtained. If desired, the transferred emulsion may be fogged and developed so that this gelatin also becomes tanned. This would happen automatically when the web containing the AgX -t-tanning developer-l-developer is subsequently exposed.

The density of the image remaining on the photomagnetic sheet is comprised of both developed silver and magnetic particles. Because the magnetic particles can contribute an appreciable density of their own, and the amount remaining is proportional to the amount of silver developed, considerable density may be obtained When only a small amount of silver halide is present in the coating. For instance, a coating containing only 40 mg. of silver per square foot can produce a developed density between 1.5 and 2.0. The density of the image transferred to the web material is contributed principally by the ferromagnetic particles until such time as the silver halide is reduced to metallic silver by printout or continued development. It desired, colored particles may be incorporated also to improve the density or control the color of the image.

The ferromagnetic particles which are required to be used in the operation of this invention must have a high magnetic permeability in order that the magnetic ield strength can be kept to a minimum. We have found that metallic particles of nickel, cobalt, and iron are useful for the purpose of this invention according to their high magnetic permeability and low magnetic susceptibility. The preferred material is called carbonyl'iron since the iron is obtained in particles having a diameter as small as three microns from iron carbonyl. However, larger particles can be used depending upon the iineness of detail desired in the image.

, The photographic emulsion may be similar to the one described in U.S. Patent 2,592,368. The emulsion comprises a mixture of substantially unhardened gelatin, silver halide, anda gelatin tanning silver halide developing agent and ferromagnetic particles. In addition, in our preferred embodiment the gelatin should have low cohesion Vand/the ability to peptize the silver halide grains, the developing agent dispersion, and the magnetic particle`s. Adhesiveness to the paper receiver while wet is not a prime requisite because this function is taken over by the, magnetic forces with more permanent bonding appearing when the sheet is dried. The ease of removal of the untanned gelatin may be increased by incorporating a gelatin extended to reduce the cohesiveness of the coating. Typical extenders are sodium alginate derivatives, sodium carboxymethyl cellulose, red sea plant extractives of U.S. application Serial No. 167,150, led January 18, 1962, and the like. The following examples are intended to illustrate our invention but not to limit it in any way.

Example 1 A silver halide emulsion coating was prepared consisting of, on each square foot, 0.099 gram 4-phenyl-catechol in a dispersion of tricresyl phosphate, 0.072 gram silver assilver chloride, 0.170 gram sodium carboxymethyl ',cellulose, 0.350 gram gelatin, and 2.0 grams carbonyl Viron-powder, grade W (manufactured by the General Grams Sodium carbonate 8 Urea 16 Water to 200 ml.

The developed negative was then pulled across the pole of a magnetron magnet, having a iield strength estimated to be about 100 gauss. The untanned gelatin, containing thc unexposed silver halide, developing agent, carboxymethyl cellulose and iron particles adhered to the magnet.

Example 2 OnV a cellulose acetate support was Coated, Per Square foot, 0.08 gram silver as silver chloride, 0.28 gram gelatin, 0.07 gram 4-phenyl catechol in aV tricresyl phosphate dispersion, and 1.0 gram carbonyl iron powder, grade W. A wetting agent was included in the coating solution.

The thus formed coated material was exposed to line copy and soaked for 8 seconds at 75 F. in an activator solution consisting of:

Grams Sodium carbonate 40 Urea Potassium bromide 5 Water to 1000 ml.

The developed negative was nally pulled across thel pole of the magnet. All the undeveloped silver halide and its surrounding gelatin, containing the developing agent and the iron powder adhered to the pole of the magnet. The image of the negative iilm was thereby stabilized.

Example 3 The coated film of Example 2 was exposed to line copy and then rolled in contact with an absorbent paper web soaked at 75 F. with the activator solution of Example 2. After 8 seconds the negative and the web were stripped apart in a magnetic eld of high gradient in the manner shown in FIGURE 5, with the magnetic attraction in the direction of the web. A developed and iixed negative photographic image was thus formed in the negative sheet and the web contained a positive image. Four point type copy was resolved on both sheets.

Example 4 y Y Gramsk Sodium carbonate 40 Urea 80 Potassium bromide 2 Water to 1000 ml.

The developed negative was fixed by pulling it across the pole of the magnet, to which the emulsion and its components from the untanned portions of the negative element adhered. Exceptionally complete removal of the unexposed areas was obtained. The remaining negaa tive image was comprised of iron powder and developed silver.

Example 5 A 'strip of coated film prepared as VVin Example 4 was exposed to line copy and rolled in contact with a paper web soaked at 75 ,F. with an activator solution consisting ofz.

. Grams Sodium hydroxide V2 Sodium carbonate 5 Urea 5 Potassium bromide 1 Water to 400 ml.

The activator solution was next warmed to F.V

and the experiment was repeated with a contact time of only one second. Identical results were obtained.

Example 6 A strip of coated iilm prepared as in Example 4 was exposed from the supportside to a continuous tone step tablet. The exposed negative was soaked at 75 F. for six seconds in an activator solution consisting of:

' Grams Sodium carbonate 40 Water to 1000 ml.

Example 7 The magnetic particles found to be operative in our invention were compared with 'y-ferric oxide particles described in U.S. Patent 2,819,963, as follows:

Cobalt, f-Ierrie nickel, iron, oxide carbonyl non Magnetic permeability High. Magnetic susceptibility Low. Hysteresis Very low. Magnetic retentivity (remanence oi residual -.-do Do.

magnetism).

Coercive force required dn llo. Magnetic saturation (in terms of field stregnth). Low High.

Iron oxides were incorporated into the photographic emulsions in place of the carbonyl iron powder and the resulting elements exposed and developed as described in Example l. None of the emulsion layers containing iron oxides yielded a separation of the unexposed tanned areas from the exposed and tanned image areas of the emulsion under the influence of a magnetic field.

Example 8 On a cellulose acetate support is coated, pei square foot, 0.08 gram silver as silver chloride, 0.28 gram gelatin, 0.07 gram 4-phenyl catechol in a tricresyl phosphate dispersion, and 3.0 grams cobalt powder having an average particle size of about microns. A wetting agent is included in the coating solution.

The thus formed coated material is exposed to line copy and soaked for 8 seconds in an activator solution consisting of:

Grams Sodium carbonate 40 Urea 8O Potassium bromide 5 Water to 1000 ml.

The developed negative is finally pulled across the pole of a Variux magnet, manufactured by the Laboratory for Science, having a field strength of about 3,00() gauss. All the undeveloped silver halide and its surrounding gelatin, containing the developing agent and the cobalt powder, adheres to the pole of the magnet. The image on the negative film is thereby developed and iixed.

Example 9 On a cellulose acetate support is coated, per square foot, 0.08 gram silver as silver chloride, 0.28 gram gelatin, 0.07 gram 4f-phenyl catechol in a tricresyl phosphate dispersion, and 3.0 grams nickel powder. A wetting agent is included in the coating solution.

The thus formed coated material is exposed to line copy and soaked for 8 seconds in an activator solution like Example 8.

The developed negative is finally pulled across the pole of the magnet. The soft gelatin containing the nickel powder adheres to the magnet, leaving a clear image on the support.

Carbonyl Iron, Type G, sold by the General Aniline and Film Corporation, is our preferred material. It is about 98 percent pure and has a weight-average diameter of about eight microns. 1t is spherical in form.

Since exposure is generally made through the base or support when a tanning development is employed, the image obtained is a negative of the original image and its left-right directions are reversed with respect to the original. When the regular development and etch-bleach treatment are employed, the exposure is from the emulsion side, and the copy kis a positive of the original and has correct orientation.

The process of our invention is most advantageously suited for line copies. If desired, copies can be made of an original by exposure in a camera in the ordinary manner or exposure can be made through a negative or positive in the usual manner. While the above examples employed a photographic gelatino-silver-halide emulsion wherein the halide was chloride, other silver halides can be employed to advantage, such as gelatino-silver-bromide, gelatino-silver-chlorobromide, gelatino-silverbro moiodide, etc., emulsions.

The concentration and'type of magnetic particles may be selected on the basis of the compatibility with the silver halide emulsions and on the field strength of the magnet available to effect the separation from the film support. The amount of silver halide utilized depends more on the amount of tanning required than on the optical density desired since the nal image density is composed of metal particles as well as silver. The developing agents which cause tanning may include also pyrocatechol, pyrogallol, and chlorohydroquinone, among others. It is not necessary that the developing agents be incorporated Within the negative emulsion; they may be in the developer solution. Solution stability, however, is greater for tanning development when the developing agents are incorporated in the emulsions.

Numerous applications or modications of our invention are possible. The purposes of simplified processing, rapid processing and the preparation of magnetizable images by photographic means are among the principal features of our invention. For instance, thermographic documentary copy processes can be provided in which a polymer containing ferromagnetic particles is softened by heat, such that if in contact with a receiver sheet, the softened colloid can be stripped to the receiver in the presence of a magnetic field. Magnetic stripping may also be used in conjunction with photoconductography. A photoconductive zinc oxide layer can be overcoated with a washed gelatin layer containing magnetic particles. Electrolytic development can be made to cause tanning of this overcoated gelatin layer, whereby the untanned portions of the gelatin layer can be removed by passing the sheet over a pole of a magnet.

Colored dyes, colored particles or pigments, color forming couplers, etc., may be incorporated in the photographic emulsion vehicle which is subject to differential hardening.

The emulsions of our invention may, of course, contain normal emulsion addenda such as chemical sensitizers, stabilizers, coating aids, etc., as are known to those skilled in the art. They will, of course, not contain hardeners. The invention has described gelatin as the vehicle but other colloids which may be differentially tanned, such as polyvinyl alcohol may be utilized, if desired.

Although specific reference has been made to Fe, Co and Ni particles, it will be realized that certain other magnetic materials such as certain complex ions, coordination compounds, alloys, nitrogen containing polymers,

7 etc.,- which have the special properties as herein described may also be utilized.

The invention'has been describedgin detail with particular reference to preferred embodiments thereof, but

it Ywill be v,understood that variations and modifications can be effected within the spirit and scope of the invention asdescribed hereinabove and as defined in the appended claims.

- We claim: 1. A method of photographic reproduction which comprises Y'developing an exposed gelatin'o-silver halide emulsion layer containing a mixture of substantially un' hardened gelatin, silver'halide, a gelatin tanning silver halide developing agent and magnetic particles selected from the 'class consisting of nickel,-cobalt and ferromagnetic particles, with an alkaline solution to obtain a'hardened gelatin, magnetic particles and silver image in the exposed areas of the emulsion'layer and substantially Vunhardened gelatin, magnetic particles and silver halide in the unexposed areas ofthe emulsion layer, said development being such as to prevent any substantial tanning of the emulsion layer in said Yunexposed areas, passing the'said emulsion layer across thepole of a magnet causing the undeveloped silver halide and its surrounding gelatin to be removed by the magnetic'leld.

2. A method of claim 1 in which the magnetic particles are,v ferromagnetic. Y

3. A method of claim 1 in which the magnetic particles are nickel.H 'e

4. A methodl of claim ticles are cobalt.

1 in which the magnetic par 5. A method of photographic reproduction which comprises developing an exposed gelatino-silver halide emulsion layer containing a mixture of substantially unhardened gelatin, silver halide and magnetic particles from the class consisting of nickel, cobalt and ferromagnetic particles in the presence of a gelatin tanning silver halide developing agent to obtain a hardened gelatin, magnetic particles and silver imagerin the exposed areas of the Y emulsion layer and substantially undhardened gelatin, magnetic particles and silver halide in the unexposed areas of the emulsion layer, said development being such as to prevent any substantial tanning of the emulsion layer in said unexposed areas, passing the said emulsion layer across the pole of a magnet causing the undeveloped silver halide and its surrounding gelatin to be removed by the magnetic field. *Y

6. A method of claim 5 in which the magnetic particles are ferromagnetic.

7. A method of claim 5 in which the, magnetic particles are nickel. y

8. A method of claim 5 in which the magnetic particles are cobalt.

References Cited in the le of this patent Y UNITED STATES PATENTS 2,740,717 Yutz et al. Apr. 3, 1956 2,819,963 Hamm Ian. 14, 1958 2,881,073 Maclay Apr. 7, 1959 3,060,025 Burg Oct. 23, 1962` 3,080,230 YHaydn L..- Mar. 5, 1963V 

1. A METHOD OF PHOTOGRAPHIC REPRODUCTION WHICH COMPRISES DEVELOPING AN EXPOSED GELATINO-SILVER HALIDE EMULSION LAYER CONTAINIGN A MIXTURE OF SUBSTANTIALLY UNHARDENED GELATIN, SILVER HALIDE, A GELATIN TANNING SILVER HALIDE DEVELOPING AGENT AND MAGNETIC PARTICLES SELECTED FROM THE CLASS CONSISTING OF NICKEL, COBALT AND FERROMAGNETIC PARTICLES, WITH AN ALKALINE SOLUTION TO OBTAIN A HARDENED GELATIN, MAGNETIC PARTICLES AND SILVER IMAGE IN THE EXPOSED AREAS OF THE EMULSION LAYER AND SUBSTANTIALLY UNHARDENED GELATIN, MAGNETIC PARTICLES AND SILVER HALIDE IN THE UNEXPOSED AREAS OF THE EMULSION LAYER, SAID DEVELOPMENT BEING SUCH AS TO PREVENT ANY SUBSTANTIAL TANNING OF THE EMULSION LAYER IN SAID UNEXPOSED AREAS, PASSING THE SAID EMULSION LAYER ACROSS THE POLE OF A MAGNET CAUSING THE UNDEVELOPED SILVER HALIDE AND ITS SURROUNDING GELATIN TO BE REMOVED BY THE MAGNETIC FIELD. 